I had a 70s Music Master myself and also did the same thing as regards keeping the original parts un-modified.I put a pair of Slowhands, Zinc baseplate on the bridge pickup, in mine along with a push/pull pot wired to put both pickups on together in series. It wasn't by any means a full humbucker sound, but it wasn't too far away and made the guitar really versatile.The Slowhands to me sounded to be quite thick in the mids, so they were by no means thin or shrill sounding.